The goal of this work is to determine the cellular mechanisms of early visual processing in the primate eye. Light-evoked electrical signals will be measured from single photoreceptors of primates. Recordings will be made with patch electrodes and suction electrodes from isolated retinas of humans and macaque monkeys. These results will be used to make a quantitative comparison to human visual abilities and limitations. The objective is to determine how the characteristics of the neural mechanisms of the eye shape our visual experience. Two major topics will be addressed. 1) Neural connectivity: What is the functional connectivity between photoreceptors in the primate eye? How does the convergence of photoreceptor signals influence wavelength coding and the detectability of dim lights? 2) Light-adaptation: What is the time course and amplitude of the electrical response to a photon and how is it altered by changes in the ambient level of illumination? How does this compare to alterations in human vision as a whole? What are the mechanisms responsible for the long-lasting excitation of rods and the rag id recovery of cone excitation following intense light? A detailed account of the electrical response properties of single retinal neurons in the primate eye is required for a better understanding of the cellular basis of clinical ERG recordings. These results will be useful for developing better diagnostic tools for the detection of retinal pathology and for the monitoring of treatments.